2 years ago I replaced the entire ignition system: plugs, wires, PCV valve, ignition coil module, optispark. The optispark finally fixed my engine hesitation problem. Now its acting up again.

It runs great until it warms up. Then the engine starts to hesitate and backfire. The SES light comes on with a code 45: Left Oxygen Sensor Circuit Rich. As soon as the SES light comes on the problem is 100% fixed Sometimes the SES light goes out and sometimes it stays on, but either way it runs fine after the SES light.

I've been running a custom PCM chip from a dynotune for 4 years which has always run a little on the rich side, but it isn't until now that I'm having problems.

What really puzzles me is the fact that the problem fixes itself after the SES light comes on.

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Background info:
1993 Corvette

Here is the list of Mods:
LT4 Hotcam, 1.6"RR, MSD Optispark, Trickflow pushrods, Cloyes Timing Chain, Ported & Polished heads, Magnaflow Mufflers, K&N Filter & Open Lid, Custom dynotune chip

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From the manual:
Any ideas? I really suck at working on cars and I don't even know where the charcoal canister is. Any help would be greatly appreciated.


Thanks

 

It really does not sound like an opti. But it has signs of the ECM going bad. You have a lot of strange stuff going on and it might relate to the ECM.

However you might want to get a scan by a pro to see if he thinks a bad O2 sensor just might be the cause.

 

Thanks for the info. That makes sense. I'm assuming that when the SES light comes on, it doesnt go into limp mode and use generic fuel tables then? I was thinking that maybe it was doing something like that. I can't find any info on what exactly happens under the condition of the SES light being on that could change things.

I will try and post a data log here from Datamaster. (Maybe I should post it in the scan and tune section?)

Thanks for your time pcolt94.

 

"any ideas"

You could always swap the O2 sensors left to right and see if the code follows the O2 sensor or stays on the left.

You could pull the fuel rail with injectors and see if any of the left bank are dripping when the rail is pressurized key on engine off.

You could remove the fuel pressure regulator's vacuum line to see if it contains wet gas after a run.

You could log data from a run and send it to your tuner.

 

Thanks for the info. I've read that swapping the O2 sensors would involve dropping the entire exhaust right?

 

I has was having the same issue with my '94. The drivers side o2 sensor was lazy. It was covered in soot when I removed it.

Replaced it with a new one and all is well. Start there.

 

Thanks man

Sounds like a plan. I'll start with the O2 sensors.

 

***UPDATE***

Replaced O2 sensors, fixed the problem 100%. Not only is the problem gone, but the engine runs much better. Pulls harder and runs smoother.

Thanks for the help guys

 

Glad your problem is gone...the reason it ran better after the SES light came on is because it was running in open loop, bypassing the O2 sensor input and just running off a premapped table on the chip. I'm guessing you noticed a considerable drop in fuel economy??

 

I was wondering that. Thanks alot for the info. That makes sense. Yes, the MPG was terrible & tons of black smoke.

Thanks